Student Loans - Narrative (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($) loan	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) loan	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 655,411,000				$ 597,374,000				$ 655,411,000	$ 597,374,000
Interest Receivable	8,164,000				8,208,000				8,164,000	8,208,000
Allowance for losses	8,522,000				7,908,000				8,522,000	7,908,000	$ 8,395,000
TDRs	3,426,000				5,187,000				3,426,000	5,187,000	$ 7,059,000
Student loan	645,825,000				588,646,000				645,825,000	588,646,000
Accrued interest receivable, charged against interest income	(8,542,000)	$ (7,468,000)	$ (7,577,000)	$ (8,580,000)	(9,276,000)	$ (9,356,000)	$ (9,302,000)	$ (9,460,000)	(32,167,000)	(37,394,000)
Student loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	57,385,000				65,800,000				57,385,000	65,800,000
Interest Receivable	$ 4,974,000				$ 5,678,000				$ 4,974,000	$ 5,678,000
Number of Loans | loan	1,297				1,505				1,297	1,505
Allowance for losses	$ 2,546,000				$ 2,091,000,000				$ 2,546,000	$ 2,091,000,000
TDRs	0				0				0	0
Student loan	513,000				386,000				513,000	386,000
Accrued interest receivable, charged against interest income									125,000	43,000
Charge-off of loans									1,947,000	740,000
Student loan | School
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	12,905,000				24,198,000				12,905,000	24,198,000
Interest Receivable	$ 3,201,000				$ 4,689,000				$ 3,201,000	$ 4,689,000
Number of Loans | loan	319				601				319	601
Student loan | Repayment, Deferment, and Forbearance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | loan	944				855				944	855
Student loan | Repayment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 28,906,000				$ 24,986,000				$ 28,906,000	$ 24,986,000
Interest Receivable	$ 292,000				$ 203,000				$ 292,000	$ 203,000
Number of Loans | loan	623				507				623	507
Student loan | Deferment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 7,407,000				$ 4,392,000				$ 7,407,000	$ 4,392,000
Interest Receivable	$ 209,000				$ 204,000				$ 209,000	$ 204,000
Number of Loans | loan	187				124				187	124
Student loan | Forbearance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 7,179,000				$ 10,626,000				$ 7,179,000	$ 10,626,000
Interest Receivable	$ 553,000				$ 188,000				$ 553,000	$ 188,000
Number of Loans | loan	134				224				134	224